Plasma surgery is a form of monopolar high-frequency surgery (HF surgery) in which a high-frequency electrical current (HF current) produced by a high-frequency generator (HF generator) is passed through an ionized noble gas (plasma), for instance argon (argon plasma), from an electrical pole within a suitably designed surgical instrument to the tissue that is to be treated by current application, and is conducted back from that site to the HF generator through a so-called neutral electrode in contact with the patient (G. Farin et al.: Technology of Argon Plasma Coagulation with Particular Regard to Endoscopic Applications; Endoscopic Surgery and Allied Technologies, No. 1, Vol. 2, February 1994, 71-77). By this means heat is introduced into the tissue, both endogenously by the HF current and exogenously because the plasma is at a higher temperature than the tissue, as a result of which the tissue temperature rises. In dependence on the temperature various thermal effects are induced in the tissue, which can be exploited by surgeons for a variety of therapeutic purposes, such as stopping bleeding (hemostasis) and/or thermal devitalization or destruction of pathological tissue (K. E. Grund et al.: Argon Plasma Coagulation in Flexible Endoscopy, Endoscopic Surgery and Allied Technologies, No. 1, Vol. 2, February 1994, 42-46).
An important physical prerequisite for plasma surgery is that a noble gas, for example the above-mentioned argon or helium, must be present between an electrical pole, formed by an electrode within the instrument, and the tissue to be treated. The reason is that noble gases can be ionized with relatively low electrical field strength, in comparison to oxygen and/or nitrogen or to air, and do not enter into chemical reactions with the tissue. Potential consequences such as carbonization or even vaporization of the tissue are thus avoided.
Within the last five years the spectrum of indications for plasma surgery, in particular when combined with flexible endoscopy, has become very broad (K. E. Grund: DMW), placing a range of new demands on the associated technology and the necessary instruments, HF generators and gas sources.
The German patent DE 198 20 240 A1 discloses a probe according to the precharacterizing clause of claim 1 that enables large-area lesions to be treated better than previously. However, especially when the plasma surgery must be employed in confined body cavities or hollow organs, the use of instruments according to DE 198 20 240 A1 can cause problems. First, with those that have only one opening on the side, it may be difficult to direct this opening toward the target tissue, i.e. the lesion for which coagulation is intended. On the other hand, when there are several openings distributed around the circumference of an instrument as specified in DE 198 20 240 A1, problems may result from unintended coagulation of parts of the tissue other than the target site. The latter can occur when the distance separating the instrument from tissues that should not or must not be coagulated is smaller than that to the target tissue.